#include<stdio.h>

int main()
{
	int n,sign;
	double s,sum=0;
	scanf("%d",&n);
	for(sign=1;sign<=n;sign++)
	{
		s=1.0/(2*sign-1);
		sum+=s;
	}
	printf("sum = %.6lf",sum);
	return 0;
}
